Digital subscriber line access multiplexers (DSLAM) typically interface a bank of modems with a broadband network. For instance, an asynchronous transfer mode (ATM) switch card in a DSLAM communicates with optical interfaces, such as trunks that interface with OC-3 fiber to a regional data center or subtends that interface with OC-3 fiber to other DSLAMs. If a network interface fails, then communication with the DSLAM is typically not possible. To improve reliability, redundant network interfaces are typically used.
One difficulty with protecting network communications through redundant network interfaces is the synchronization of data transfers when a failed network interface is protected by a backup network interface. Without synchronization, switching to a back-up network interface is more difficult. For instance, failure of a network interface leads to complete switching to another network interface so that each network interface typically only supports a single type of physical port.